Challenge


Historically, this section of Lake Forest shoreline was eroding and was not able to protect the existing park and natural resources. All the recreational activities were threatened by the coastal erosion.

Solution


The Lake Forest Illinois Park Commission commissioned design studies for the project and construction was completed in 1987 during high water levels. The implemented shoreline protection system consists of rubblemound breakwaters and beach cells working together. The breakwaters reduce the incoming wave energy and contain the beach sand; the beach dissipates the wave energy and provides an important recreational component.

GZA was commissioned to assess the existing beach and structure conditions and design an appropriate program to supplement new sand to the north beach cell as a pilot project. The intent is to apply the same design to all the other project areas. This work included a detailed assessment of the beach, breakwaters, data analysis, wave run-up calculations, and development of recommendations for operational maintenance and repair priorities over a 10-year timeframe. The project was initially constructed with quarry coarse sand (called Bird’s Eye). With time, a material contamination with fine sand was documented, which flattened the beach slope and increased the wave run-up and damage to the walkway and parking area. A combination of Torpedo sand (medium) and Bird’s Eye (coarse) was designed for the project and submitted for regulatory approval. The construction is expected in September 2022. A technical study for an underwater berm as a sill structure is being conducted to increase the beach retention time, thus reducing the long-term beach nourishment events. The berm will break the incoming storm waves and reduce the energy reaching the shoreline/sandy beach.

Benefit


The team led by Dan Veriotti, PE carefully analyzed and designed the proposed improvements, assisting with budgetary planning for near- and long-term.